873 research outputs found
QCD critical point and event-by-event fluctuations in heavy ion collisions
A summary of work done in collaboration with K. Rajagopal and E. Shuryak. We
show how heavy ion collision experiments, in particular, event-by-event
fluctuation measurements, can lead to the discovery of the critical point on
the phase diagram of QCD.Comment: 4 pages. Summary of work done in collaboration with K. Rajagopal and
E. Shuryak (hep-ph/9903292). To be published in the proceedings of Quark
Matter 99, Torino, Italy, May 10-14, 199
Dirac operator as a random matrix and the quenched limit of QCD with chemical potential
The behavior of quenched QCD at nonzero chemical potential has been a
long-standing puzzle. An explicit solution is found using the random matrix
approach to chiral symmetry breaking. At nonzero the quenched QCD is not
a simple limit of a theory with quarks: a naive `replica trick'
fails. A limit that leads to the quenched QCD is that of a theory with
quarks: quarks with original action and quarks with conjugate action.Comment: 3 pages, espcrc, 2 figures. Talk presented at LATTICE96(finite
temperature
The Phase Diagram of QCD
We show that current experimental knowledge of QCD together with general
model independent arguments such as continuity, universality and thermodynamic
relations, as well as the information gained from various models can be used to
constrain the phase diagram of QCD as a function of temperature and baryon
chemical potential.Comment: 6 pages; to appear in Proceedings of the Intl Workshop on QCD at
Finite Baryon Density, Bielefeld, Germany, April 199
Non-Gaussian fluctuations near the QCD critical point
We study the effect of the QCD critical point on non-Gaussian moments
(cumulants) of fluctuations of experimental observables in heavy-ion
collisions. We find that these moments are very sensitive to the proximity of
the critical point, as measured by the magnitude of the correlation length xi.
For example, the cubic central moment of multiplicity ~ xi^4.5 and the quartic
cumulant ~ xi^7. We estimate the magnitude of critical point contributions to
non-Gaussian fluctuations of pion and proton multiplicities.Comment: 4 pages, 3 figure
Hydro+: hydrodynamics with parametric slowing down and fluctuations near the critical point
The search for the QCD critical point in heavy-ion collision experiments
requires dynamical simulations of the bulk evolution of QCD matter as well as
of fluctuations. We consider two essential ingredients of such a simulation: a
generic extension of hydrodynamics by a_parametrically_ slow mode or modes
("Hydro+") and a description of fluctuations out of equilibrium. By combining
the two ingredients we are able to describe the bulk evolution and the
fluctutations within the same framework. Critical slowing down means that
equilibration of fluctuations could be as slow as hydrodynamic evolution and
thus fluctuations could significantly deviate from equilibrium near the
critical point. We generalize hydrodynamics to partial-equilibrium conditions
where the state of the system is characterized by the off-equilibrium magnitude
of fluctuations in addition to the usual hydrodynamic variables -- conserved
densities. We find that the key element of the new formalism -- the extended
entropy taking into account the off-equilibrium fluctuations -- is remarkably
similar to the 2PI action in quantum field theory. We show how the new Hydro+
formalism reproduces two major effects of critical fluctuations on the bulk
evolution: the strong frequency dependence of the anomalously large bulk
viscosity as well as the stiffening of the equation of state with increasing
frequency or wave-number. While the agreement with known results confirms its
validity, the fact that Hydro+ achieves this within a local and deterministic
framework gives it significant advantages for dynamical simulations.Comment: 46 pages, 5 figure
Acceptance dependence of fluctuation measures near the QCD critical point
We argue that a crucial determinant of the acceptance dependence of
fluctuation measures in heavy-ion collisions is the range of correlations in
the momentum space, e.g., in rapidity, . The value of
for critical thermal fluctuations is determined by
the thermal rapidity spread of the particles at freezeout, and has little to do
with position space correlations, even near the critical point where the
spatial correlation length becomes as large as fm (this is in
contrast to the magnitudes of the cumulants, which are sensitive to ).
When the acceptance window is large, , the
cumulants of a given particle multiplicity, , scale linearly with
, or mean multiplicity in acceptance, , and
cumulant ratios are acceptance independent. While in the opposite regime,
, the factorial cumulants, ,
scale as , or . We demonstrate this general
behavior quantitatively in a model for critical point fluctuations, which also
shows that the dependence on transverse momentum acceptance is very
significant. We conclude that extension of rapidity coverage proposed by STAR
should significantly increase the magnitude of the critical point fluctuation
signatures.Comment: 9 pages, 4 figures, references adde
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